1. Field of the Invention
This disclosure generally relates to encoders, and more particularly to detection of failures in increment encoders.
2. Description of the Related Art
Increment encoders are used to determine the rotational velocity, acceleration, direction and/or the position of a rotating object in a machine, such as a shaft of an electric motor or generator. This information can be used to control the machine. For example, in electric/hybrid motor vehicles information from an encoder is typically provided to a control unit that can use the information together with other information to control the motor vehicle.
A failed encoder can lead to abnormal behaviors of a machine. Thus, methods for detecting and responding to the failure of an encoder have been developed. For example, a control unit can be programmed to generate appropriate control signals in response to an indication that an encoder has failed, such as control signals shutting down a machine, such as a motor vehicle.
Conventional methods of detecting encoder failure are directed to detecting failure above a certain threshold rotational speed because failures at a zero rotational speed are difficult to detect due to challenges in measuring low rotational speeds. The threshold minimum rotational speed will vary based on the characteristics of a particular machine. Conventional error detection schemes also are likely to produce many inaccurate indications of encoder failure at a zero rotational speed, which also is undesirable.